I see there's a consistent issue with IPv6 for F root anycast instance in Chennai hosted at NIXI - 2001:500:2f::f

If I trace it from the RIPE Atlas anchor, I get following:

Probe #6107

1 2401:7500:fff0:1::1 0.838 ms 0.747 ms 0.632 ms

2 2400:5200:1c00:d::1 1.755 ms 1.745 ms 1.726 ms

3 2403:0:100::2be 2.089 ms 2.054 ms 2.049 ms

4 2404:a800:2a00::13d 45.589 ms 26.274 ms 33.64 ms

5 2404:a800::178 26.376 ms 25.406 ms 25.276 ms

6 2001:de8:1:2::3 25.363 ms 25.232 ms 25.223 ms

7 * * * *

8 * * * *

9 * * * *

10 * * * *

11 * * * *

6th hop is ISC's router on NIXI Chennai peering fabric (2001:de8:1:2::/64). Clearly, there's an issue in return path and possibly setup is either without default or misconfigured IPv6 or partial table.

on "sh bgp ipv6 sum" on NIXI Chennai route server, it gives:

2001:de8:1:2::3 24049 ESTAB 25d 3h10m 1 0 2263 0

2001:de8:1:2::4 24049 ESTAB 125d18h30m 1 0 2264 0

show ipv6 bgp neighbors 2001:de8:1:2::3 received-routes

There are 1 received routes from neighbor 2001:de8:1:2::3

Searching for matching routes, use ^C to quit...

Status A:AGGREGATE B:BEST b:NOT-INSTALLED-BEST C:CONFED_EBGP D:DAMPED

E:EBGP H:HISTORY I:IBGP L:LOCAL M:MULTIPATH m:NOT-INSTALLED-MULTIPATH

S:SUPPRESSED F:FILTERED s:STALE

Prefix Next Hop MED LocPrf Weight Status

1 2001:500:2f::/48 2001:de8:1:2::3 10 100 0 BE

AS_PATH: 24049 3557

show ipv6 bgp neighbors 2001:de8:1:2::4 received-routes

There are 1 received routes from neighbor 2001:de8:1:2::4

Searching for matching routes, use ^C to quit...

Status A:AGGREGATE B:BEST b:NOT-INSTALLED-BEST C:CONFED_EBGP D:DAMPED

E:EBGP H:HISTORY I:IBGP L:LOCAL M:MULTIPATH m:NOT-INSTALLED-MULTIPATH

S:SUPPRESSED F:FILTERED s:STALE

Prefix Next Hop MED LocPrf Weight Status

1 2001:500:2f::/48 2001:de8:1:2::4 10 100 0 E

AS_PATH: 24049 3557

One should possible stop this BGP announcement until return path issue is fixed.